A leaf spring suspension system is a common form of suspension system. Leaf spring suspension systems can be used in many applications, including stationary conveyor systems and many other systems sensitive to mechanical vibrations. However, the most common use of leaf spring suspension systems is for commercial vehicles such as trucks, vans, and other large payload vehicles.
In particular, vehicle suspensions have commonly used leaf spring assemblies to resiliently support the axle relative to the frame and to carry loads on the axle fore and aft to frame-mounted supporting devices. Generally, a leaf spring assembly is pivotally connected at one end to a bracket rigidly mounted on the frame of the vehicle in a manner such that the leaf spring is free to rotate about a fixed pivot relative to the frame when the axle moves vertically. The other end of the leaf spring assembly is connected at another end to a second bracket also rigidly mounted to the frame of the vehicle. However, it is desirable that this connection at the rear end of the leaf spring have a double rotatable configuration (i.e., have two parallel axes of rotation) to help prevent buckling of the leaf spring as the axle moves relative to the frame and deflection of the leaf spring causes the spring to change its horizontal length. As a result, one or more shackles or links are generally used which are pivotally attached at their top ends to the second bracket and are pivotally attached at their bottom ends to the leaf spring. In this manner, the rear end of the leaf spring assembly is still pivotally attached to the axle, but also may still move in the fore and aft directions relative to the frame of the vehicle to help prevent buckling of the leaf spring.
The most common mechanism for mounting a leaf spring suspension system utilizes caps and pinch bolts to secure the spring pins and shackles used. In particular, the front end of a leaf spring assembly is pivotally connected to the front bracket using a spring pin rotatably attached to the front end of the leaf spring and to the front bracket. The spring pin is secured in place using a fitted cap that is attached to one end of the spring pin such that lateral movement of the spring pin relative to the leaf spring and the front bracket is prevented.
The rear end of the leaf spring assembly is connected in a double rotatable configuration to the rear bracket using two spring pins, two shackles, four pinch bolts, and two caps. One spring pin is rotatably attached to the rear end of the leaf spring and one spring pin is rotatably attached to the rear bracket. Each spring pin in the cap and pinch bolt mounting apparatus has a semi-circular groove near both ends of the spring pin, wherein the axis of each semi-circular groove is substantially perpendicular to the longitudinal axis of the spring pin. Two shackles are used wherein each shackle links one end of one spring pin to a corresponding end of the other spring pin. Each shackle has a central body portion and two ends; each end comprises two arms forming a substantially cylindrical hole but the arms do not form a complete cylinder in that the arms do not contact each other at the end farthest from the central body portion. Each end also has a bolt hole passing through both arms in a direction perpendicular to the substantially cylindrical hole such that the diameter of the substantially cylindrical hole can be reduced by threading a bolt through the bolt holes in the arms and tightening the bolt. Additionally, the bolt hole is oriented such that a bolt passing through both arms partially enters the substantially cylindrical hole formed by the arms. When assembled, a spring pin is aligned through the substantially cylindrical hole formed by the arms of the shackle such that a bolt threaded through the bolt hole in the arms of the shackle is aligned with the semicircular groove near the end of the spring pin, and the bolt is tightened to form an interference fit between the spring pin and the shackle. In this manner, the spring is prevented from rotating relative to the shackle and is prevented from moving laterally relative to the shackle. In applications using this type of mounting apparatus, each shackle requires this assembly to be performed two separate times. Because two shackles are used to mount the leaf spring suspension system, one on each side of the leaf spring and the rear bracket, this assembly must be performed four times with four different bolts. Finally, a cap is placed on the end of each spring pin to further secure the spring pins in place.
Although the cap and pinch bolt apparatus for mounting a leaf spring suspension system does secure the suspension system to the frame, it is difficult and costly to utilize such an apparatus because of the amount of parts necessary for mounting the suspension. A mounting apparatus that utilizes fewer parts would be provide the following advantages: lower cost, simpler and easier installation and maintenance, lower weight, and a decreased probability of failure. For obvious reasons, fewer parts results in lower cost, simpler and easier installation and maintenance, and lower weight. Additionally, the probability of failure of an apparatus having fewer parts is statistically reduced. Therefore, a need exists to improve upon the cap and pinch bolt apparatus by reducing the number of parts necessary to mount a leaf spring suspension system.
As vehicle innovations progress, one of the continuing goals is to make a lighter vehicle that can still carry the same payload as before. To achieve this goal, often lightweight materials are incorporated, such as various aluminum alloys. With the use of such lightweight materials however, there are other drawbacks. Often, one of the drawbacks of lightweight materials is that their hardness typically is not as high as the hardness of traditionally used materials, i.e. steel. In the past suspension components (shackles, leaf springs, and suspension brackets) were almost exclusively made of steel. But if these suspension components are made of a lightweight material that has a hardness less than the hardness of the typical steel materials used, then steel wear washers located between these suspension components will not wear. Instead, the suspension components made of a material having a hardness less than that of the steel wear washers will be worn. Wear of the other suspension components rather than the wear washers is typically not desirable because the purpose of the wear washers is to wear as the parts move against each other during operation. This prolongs the life of the suspension components because the wear washers are inexpensive to replace relative to other suspension components. Thus, with implementation of new designs that incorporate lightweight materials, there is a need for a wear washer that will wear before the other suspension components.